Some forms of multi-carrier transmission are composed of a number of independent signals centered on different frequencies. In some multi-carrier communication systems signals are combined together as a vector. An inverse fast Fourier transform (IFFT) can be performed on the vector to produce a discrete time domain signal which is converted to a continuous time domain signal and transmitted. Such a transmitted analog signal can contain a number of peaks, some of which can exceed component and/or other capabilities of the system.
In a DSL environment the level distribution on the line is quasi Gaussian. This means that the peak-to-average ratio (PAR) (where the peak is defined as the level above which the probability to reach such level is 10−7) is 5.2. This presents significant challenges to the design of the analog components (e.g., drivers, data converters, etc.) that are required to accommodate or supply high signal levels that occur only a fraction of the time. Attempts have been made to find methods to reduce the PAR in the transmit path (see, for example, U.S. Pat. No. 6,314,146 and U.S. Pat. No. 6,424,681, which are incorporated herein by reference for all purposes), but comparable efforts do not appear to have not been expended on PAR reduction in the receive path.